To simplify my life, I'm continuously trying to standardize the software configuration of all physical and virtual Linux installations I'm administering. In terms of Linux distributions, I've already reduced the previous diversity to ArchLinux and Debian Sid/Testing. As window manager, I'm using either wmii or OpenBox. The former is started via startx and a corresponding entry in ~/.xinitrc, but what about the latter? Well, of course, I'm using a display manager to start it.

But which one? For some (probably historical) reason, I've set up my four systems with three different display managers: lxdm, lightdm, and slim, and of course I've no idea which system is actually employing which display manager. Surely, the Swiss knife of system information should know.

Since I'm also using systemd, /etc/systemd/system/display-manager.service contains the required information. Debian-based systems offer in addition /etc/X11/default-display-manager. And for those not using systemd: you should know what you're doing anyway.